The semi-official (worked on by folks involved with the core product from, as far as I can tell, early on, but not released by Slack like core Nebula is) mobile

The semi-official (worked on by folks involved with the core product from, as far as I can tell, early on, but not released by Slack like core Nebula is) mobile clients don't have a license associated with them, which is a bit of a blocker to further development or distribution on certain stores (FOSS-only ones, for instance, and really no-one else can distribute them at all right now without risk).